Arc furnaces used for steel making are usually connected to two or three phase AC networks powdered by generators.
During the meltdown stage in particular, arc furnaces subject their power supply systems to difficult load problems. The reactive power fluctuations are great and cause voltage fluctuations normally compensated by reactive power compensation, such as by static systems comprising thyristor-connected capacitors or phase-angle controlled reactors with the compensation possibly completed by harmonic filters. A phase-angle controlled reactor normally consists of a number of single-phase air reactors, one for each phase of the current.
Such compensating means cannot compensate the active power fluctuations, although the active power may be balanced.
In relatively weak networks, the active power fluctuations give rise to disturbing power fluctuations despite compensation of the reactive power fluctuations. When arc furnaces are connected to such networks in the vicinity of the power generators, these active power fluctuations may be detrimental to the generators as well as their driving turbines. Current asymmetries and power fluctuations are severe problems.
Arc furnaces are customarily charged with cold scrap, and during the meltdown stage the arcs consume substantial power while raising the temperature of such charges to melting temperatures.
The object of this invention is to reduce the effect of the active power fluctuations on the network, and in addition, to preheat the scrap so that when charged in an arc furnace its meltdown requires less arc power consumption.